2019 3 12
The effects of temperature on enzyme activity [@q10]. Top - increasing temperature increases the rate of reaction (Q10 coefficient). Middle - the fraction of folded and functional enzyme decreases above its denaturation temperature. Bottom - consequently, an enzyme's optimal rate of reaction is at an intermediate temperature.
Green frog on blue surface.
Overview of feed energy flow through the animal body
Infrared cameras image that cows generating the heats. @kim2018image developed the algorithms for tracking the cows using IR camera video.
| Animal | Normal temperature (°C) | Animal | Normal temerature (°C) |
|---|---|---|---|
| Cattle | 38.5 | Donkey | 38.2 |
| Calf | 39.5 | Chicken | 42.0 |
| Buffalo | 38.2 | Camel | 34.5-41.0 |
| Sheep | 39.0 | Horse | 38.0 |
| Llama, alpaca | 38.0 | Pig | 39.0 |
| Goat | 39.5 | Piglet | 39.8 |
| Methods | Cooling | Heating |
|---|---|---|
| Convection | Increasing blood flow to body surfaces | Entering a warm water or air current; Building an insulated nest or burrow |
| Conduction | Lying on cool ground; Staying wet in a river, lake or sea; Covering in cool mud | Lying on a hot surface |
| Radiation | Get away from the sun | Lying in the sun; Folding skin to reduce exposure |
\(THI = (0.8*T) + [H*(T - 14.4)] + 46.4\)
where T is the air temperature and H is the relative humidity.
THI chart for dairy cows.
The relationship between the immediate effects of environmental heat stress and the 3 key constructs of animal welfare.
Fan installations, which facilitate air movement and increase convection, have been used to reduce environmental temperatures and mitigate heat stress by decreasing respiratory rate and rectal temperature and increasing DMI (Armstrong, 1994).
High-pressure mist injected into fans (which function to cool the microclimate air that the cows inspire) or large water droplets from low-pressure sprinkler systems that completely wet the cow by soaking the hair coat.
Physical structures that provide shade such as trees, roofs, or cloth can create more hospitable microclimates for cows because of the reduction in solar radiation exposure and decline in ambient temperature.
Barn orientation (depending on geographic location) can also help mitigate heat stress by reducing the insolation and stall surface temperature.
As temperatures heat up during the summer cattle producers need to assess the heat stress that their cattle are under. Typically pastured cattle are not as susceptible to heat stress as feedlot cattle. Pastured cattle have the ability to seek shade, water and air movement to cool themselves.
Compared to other animals cattle cannot dissipate their heat load very effectively. Cattle do not sweat effectively and rely on respiration to cool themselves. Cattle should not be worked during times of extreme heat and only early in morning when it is hot.
Cattle’s core temperature peaks 2 hours after peak environmental temperature. It also takes at least 6 hours for cattle to dissipate their heat load. Therefore, if peak temperature occurred at 4:00 pm cattle will not have recovered from that heat load until after 12:00 am and it will be later than that before cattle have fully recovered from the entire days heat load. Special attention should be paid to cattle with increased risk of heat stress including heavy cattle, black cattle and respiratory compromised animals.
The water requirements of cattle increases during heat stress. Cattle lose water from increased respiration and perspiration. Consumption of water is the quickest method for cattle to reduce their core body temperature.
Heat production from feed intake peaks 4 to 6 hours after feeding. Therefore heat production in cattle fed in the morning will peak in the middle of the day when environmental temperatures are also elevated. Changing the ration indicates that lowering the energy content of diet will decrease the heat load. The general recommendation is to reduce the diet energy content by 5 to 7%.
Increasing the air flow can help cattle cope with extreme heat events. Wind speed has been shown to be associated with ability of cattle to regulate their heat load.
Sprinklers can be used to cool cattle during times of stress. Sprinklers increase evaporative cooling and can reduce ground temperature. Sprinklers should thoroughly wet the animal and not just mist the air in order to cool the animal. Sprinklers should be placed away from feed bunks and waterers. Cattle need to be introduced to sprinklers prior to extreme heat.
Most animals can transfer internal heat to the outside of the body by sweating and panting. These are the two most important tools for the maintenance of body temperature and form their inbuilt evaporative cooling system. However, pigs do not sweat and have relatively small lungs. Due to these physiological limitations and their relatively thick subcutaneous fat, pigs are prone to heat stress. Today’s modern pig genotypes produce considerably more heat than their predecessors (new genetic lines of pigs produce nearly 20% more heat than their counterparts in the early 1980s.).
The two obvious symptoms observed when pigs are exposed to heat stress are increased respiration rate and loss of appetite. If the pig exposed to 35°C for 24 hours significantly damaged the intestinal defense system and also increased plasma endotoxin levels. It can provide an opportunity for infection as pathogenic bacteria can invade the body more easily.
High temperature affects the physiological functions of poultry birds at any stage of life which in results affects the poultry production performance. Modern commercial poultry produces more body heat due to their fast metabolism. This makes birds more sensitive to environmental temperature. In addition, the chicks are highly sensitive to heat stress because they don't have sweat glands.
When a dog is exposed to high temperatures, heat stroke or heat exhaustion can result. Heat stroke is a very serious condition that requires immediate medical attention. Dogs do not sweat through their skin like humans. They release heat primarily by panting and they sweat through the foot pads and nose. If a dog cannot effectively expel heat, the internal body temperature begins to rise. Once the dog’s temperature reaches 41°C damage to the body’s cellular system and organs may become irreversible.
Signs of heat stroke are 1) increasing the rectal temperature, 2) vigorous panting, 3) dark red gums, 4) tacky or dry mucus membranes (specifically the gums), 5) lying down and unwilling (or unable) to get up, and/or 6) dizziness or disorientation.
Certain types of dogs are more sensitive to heat – especially obese dogs and short-nosed breeds, like Pugs and Bulldogs.